Antiozonant mixture containing a phenylenediamine and a n-alkyl-aminophenol or a n-alkyl-alkoxyaniline



United States Patent US. Cl. 252-403 8 Claims ABSTRACT OF THE DISCLOSURE Synergistic mixture of phenylenediamine antiozonant and N-substituted-aminophenol or N-substituted-alkoxyaniline.

BACKGROUND OF THE INVENTION Certain phenylenediamine derivatives have been found to be very active antiozonants in rubber. However, there always is a need for even further increasing the potency of antiozonants. The increased potency permits either the use of a lower concentration of the antiozonant to obtain a predetermined stability or it will afford greater stability to the rubber when used in an equal concentration.

DESCRIPTION OF THE INVENTION This invention relates to a novel synergistic mixture. The increased stability obtained by the novel mixture is surprising because it would not be expected that such a mixture would have a potency greater than that obtained by either component alone.

In one embodiment the present invention relates to a mixture of a phenylenediamine antiozonant and a compound of the following formula where R and R are hydrogen or alkyl, R is hydrogen, alkyl or cycloalkyl and R is alkyl or cycloalkyl.

In another embodiment, the present invention relates to the use of the above mixture as an additive to rubber.

As hereinbefore set forth, one component of the mixture of the present invention comprises a phenylene-diamine antiozonant. In one embodiment the phenylenediamine antiozonant is an N,N'-di-sec-alkyl-p-phenylenediamine in which each alkyl contains from 3 to about 20 carbon atoms and more particularly from 3 to 10 carbon atoms. Illustrative preferred examples in this embodiment include N,N'-diisopropyl-p-phenylenediamine, N,N'-secbutyl-p-phenylene-diamine, N,N-sec-pentyl-p-phenylenediamine, N,N'-sec-hexyl-p-phenylenediamine, N,N'-secheptyl-p-phenylenediamine, N,N-sec-octyl-p-phenylenediamine, N,N'-sec-nonyl-pphenylenediamine and N,N'-secdecyl-p-phenylenediamine.

In another embodiment the phenylenediamine antiozonan-t is an N-alkyl-N-phenyl-p-phenylenediamine in which the alkyl contains from 3 to about and more particularly from 3 to 10 carbon atoms. Illustrative preferred examples include N-isopropyl-N-phenyl-pphenylenediamine, N-sec-butyl-N-phenyl-p-phenylenediamine,

N-sec-pentyl-N'-phenyl-p-phenylenediamine, N-sec-hexyl- N'-phenyl-p-phenylenediamine, N-sec-heptyl-N'-phenyl-pphenylenediamine, N-sec-octyl-N'-phenyl-p-phenylenediamine, N-sec-nonyl-N'-phenyl-p-phenylenediamine and N- sec-decyl-N'-phenyl-p-phenylenediamine.

Other phenylenediamine antiozonants include N,N'-dicycloalkyl-p-phenylenediamine and more particularly N,N-dicyclohexyl-p-phenylenediamine. It is understood that mixtures of the phenylenediamine antiozonants may be used.

As hereinbefore set forth, the phenylenediamine antiozonant is used in admixture with a compound of the formula hereinbefore set forth. When R and R are hydrogen in the above formula, the compound is an N-substituted-p-aminophenol. Illustrative compounds in this embodiment include N-alkyl-p-aminophenol. The alkyl group may contain from 1 to 20 or more carbon atoms and thus will be selected from methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, octadecyl, nonadecyl, eicosyl, etc. In a preferred embodiment, the alkyl group is of secondary configuration. Illustrative preferred compounds in this embodiment include N-isopropyl-p-aminophenol, N-sec-butyl-p-aminophenol, N-secpentyl-p-aminophenol, N-sec-hexyl-p-aminophenol, N-secheptyl-p-aminophenol, N-sec-octyl-p-aminophenol, N-secnonyl-p-aminophenol, N-sec-decyl-p-aminophenol, etc. In another embodiment, the alkyl group is of primary configuration and illustrative compounds include N-methylp-aminophenol, N-n-propyl-p-aminophenol, N-n-butyl-paminophenol, N-n-pentyl-p-aminophenol, N-n-hexyl-paminophenol, N-n-heptyl-p-aminophenol, N-n-octyl-paminophenol, N-n-nonyl-p-aminophenol and N-n-decyl-paminophenol.

When R is alkyl, the compound is an N,N-dialkyl-paminophenol. In one embodiment, R" is an alkyl of from 1 to 4 carbon atoms and R' is an alkyl of from 3 to about 20 carbon atoms. Illustrative compounds in this embodiment include N-methyl-N-isopropyl-p-aminophenol, N-methyl-N-sec-butyl-p-aminophenol, N-methyl-N- sec-pentyl-p-aminophenol, N-methyl-N-sec-hexyl-p-aminophenol, N-methyl-N-sec-heptyl-p-aminophenol, N-methyl N-sec-octyl-p-aminophenol, N-methyl-N-sec-nonyl-p aminophenol, N-methyl-N-sec-decyl-p-aminophenol, and similar compounds in which the methyl group is replaced by ethyl, propyl or butyl. Here again it is understood that the alkyl groups may be of primary or secondary configuration.

Where at least one R" and R is cycloalkyl, illustrative compounds include N-cyclohexyl-p-aminophenol, N,N-dicyclohexyl-p-aminophenol, N-methyl-N-cyclohexyl-p-aminophenol, N-ethyl-N-cyclohexyl-p-aminophenol, N-propylbutyl-N-cyclohexyl-p-aminophenol, etc. While cyclohexyl is a preferred cycloalkyl substituent, it is understood that the cycloalkyl group may contain from 3 to 12 or more carbon atoms and thus be selected from cyclopropyl, cyclobutyl cyclopentyl, cycloheptyl, cyclooctyl, cyelononyl, cyclodecyl, cycloundecyl, cyclododecyl, etc.

When R in the above formula is alkyl, the compound is an N-substituted alkoxyaniline in which the alkoxy group preferably contains from one to 20 and more particularly from 1 to 12 carbon atoms and the other substituents are selected from those hereinbefore set forth. Illustrative compounds in this embodiment include N- isopropyl-p-anisidine, N-sec-butyl-p-anisidine, N-sec-pentyl-p-anisidine, N-sec-hexyl-p-anisidine, N-sec-heptyl-panisidine, N-sec-octyl-p-anisidine, N-sec-nonyl-p-anisidine, N-sec-decyl-p-anisidine, N-sec-undecyl-p-anisidine, N-secdodecyl-p-anisidine, etc. N-methyl-N-isopropyl p anisi- 3 dine, N-methyl-N-sec-butyl-p-anisidine, N-methyl-N-secpentyl-anisidine, N-methyl-N-sec-hexyl-anisidine, bl-methyl-N-sec-heptyl-anisidine, N-methyl-N-sec-octyl-anlsidine, etc., corresponding compounds in which the sec-alkyl group is replaced by n-alkyl group, corresponding compounds in which the methyl group is replaced by ethyl, propyl or butyl, corresponding compounds in wh1ch the methoxy group is replaced by ethoxy (the compound being an N-substituted p-phenetidine), propoxy, butoxy, pentoxy, hexoxy, heptoxy, octoxy, nonoxy, decoxy, etc.

When at least one of R" and R is cycloalkyl and particularly cyclohexyl, illustrative compounds include N cyclohexyl-p-anisidine, N,N-dicyclohexyl-p-anisidine, N-alkyl-N-cyclohexyl-p-anisidine, and corresponding compounds in which the alkyl and alkoxy groups are selected from those hereinbefore set forth. It is understood that mixtures of N-substituted-p-aminophenols and/ or N- substituted-p-alkoxyanilines may be used.

The phenylene antiozonants are prepared in any sultable manner and the prior art is replete with examples of such preparations. The substituted p-aminophenol or substituted alkoxyanilines are prepared in any suitable manner. For example, N-sec-alkyl-p-aminophenol 1s prepared by the reductive alkylation of p-nitrophenol or p-aminophenol with a ketone for the preparation of the sec-alkyl derivatives or with an aldehyde for the preparation of the n-alkyl derivatives. Similarly, the N-substituted-alkoxyanilines may be prepared by the reductlve alkylation of p-anisidine, p-phenetidine, etc., or the .corresponding nitro-derivative with the ketone or aldehyde. When the nitrogen atom is to contain 2 substituents, the reductive alkylation is effected in 2 stages, utilizlng different ketones in each stage. For example, N-methyl- N-sec-butyl-p-aminophenol or p-anisidine is prepared by reductive alkylation using methyl ethyl ketone in the first stage and formaldehyde in the second stage.

The reductive alkylation is effected in any suitable manner and generally under a hydrogen pressure of from about 100 to 3,000 p.s.i. or more and particularly of from about 1,000 to about 2,000 p.s.i., and a temperature of from about 200 to about 500 F. or more and particularly of from 250 to about 500 F. Generally, the reductive alkylation is effected by using an excess of the ketone or aldehyde and this excess may run from 2 to about 20 or more and particularly from 3 to about 8 moles thereof per mole of aminophenol, alkoxyaniline or correesponding nitro-derivative. Any suitable reductive alkylation catalyst is used. One catalyst comprises an intimate mixture of copper oxide, chromium oxide and barium oxide. Other catalysts include those containing nickel, molybdenum, platinum and/or palladium. A particularly preferred catalyst comprises a composite of alumina with from about 0.1% to or more of platinum, which composite may or may not contain chlorine and/or fluorine in a total concentration of from about 0.2% to 5% or more by Weight of the composite.

Where R in the above formula is alkyl, the alkyl group will be selected from methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, and dodecyl, etc. It is understood that 2 or more of such alkyl groups may be attached to the ring.

As hcreinbefore set forth, the components of the mixture are used in synergistic proportions. In one embodirtnent these may comprise from about 5% to about 95% of one component and from about 95% to about 5% of the other component. In most cases it is preferred to utilize these components in concentrations of from about 25% to about 75% of one component and from about 75% to about 25 of the other component. In a particularly preferred embodiment, the p-phenylenediamine antiozonant comprising from 50% to 90% and the N- substituted aminophenol or N-substituted alkoxyaniline 4 comprises from about 50% to about 10% by weight of the synergistic mixture.

The synergistic composition of the present invention is used in rubber in a concentration sufficient to effect the desired stabilization. The concentration may range from about 0.5 to about 5% and more particularly from about 1.5% to 4% by weight of the rubber, although, in some cases higher or lower concentrations may be employed. These concentrations are based on the rubber hydrocarbon exclusive of the other components of the rubber composition and are used in this manner in the present specifications and claims. When desired, the synergistic mixture may be used along with an additional antioxidant and also is used along with other additives incorporated in rubber for specific purposes including accelerators, softeners, extenders, wax, reinforcing agents, etc.

When used along with an additional antioxidant, it is understood that any suitable antioxidant may be employed including, for example, 2,6-di-tert-butyl-4-methylphenol, phenyl beta-naphthylamine, 6-phenyl-2,2,4-trimethyl-1,2- dihydroquinoline, marketed under the trade name of Santoflex B 2,2 methylene bis(4-methyl-6-tert-butylphenol), 2,6-di-tert-butyl-p-cresol, the reaction product of acetone and diphenylamine, marketed under the trade name of B-L-E., etc. These antioxidants generally are used in a concentration of from about 0.5% to about 3% by weight of the rubber.

When desired, the synergistic mixture of the present invention also is used along with paraffin and/or microcrystalline wax. The wax generally is utilized in a concentration of from 0.5% to 3% by weight of the rubber.

In one embodiment the components of the synergistic mixture are added separately to the rubber formula. In another and preferred embodiment the components of the synergistic mixture are combined and then added to the rubber formula. In still another embodiment the synergistic mixture is admixed with the additional antioxidant, wax and/or other additives, and the mixture then is composited with one or more of the other components of the rubber formulation. In a preferred embodiment the synergistic mixture is incorporated in the latex prior to milling. In still another embodiment vulcanized rubber may be soaked, dipped or suspended in the synergistic mixture to apply a surface coating to the rubber, or the synergistic mixture may be sprayed, poured or otherwise contacted with the previously vulcanized rubber.

The synergistic mixture of the present invention is utilized in any rubber formulation subject to ozone cracking, including those used for autmobile and truck tires and tubes, hose, belting, sheet and thread rubber, rubberized .fabrics, molded goods, boots and shoes, etc. whether vulcanized in a mold, in open steam, in hot air, or in the cold by the so-called acid process. In another embodiment, the present invention can be utilized for the stabilization of adhesives, elastomers, etc., which tend to crack due to ozone.

When the synergistic mixture is added to a liquid such as rubber pigment or an oil, it is dissolved therein in the desired proportions. When the synergistic mixture is added to a solid substrate, it is incorporated therein by milling, mastication, etc. The synergistic mixture may be utilized as such or as a solution or dispersion or as a powder, paste, etc.

In general, rubber is classified as a vulcanizable diene hydrocarbon rubber and comprises polymers of conjugated 1,3-dienes either as polymers thereof or as copolymers thereof with other polymerizable compounds. In one embodiment the rubber is a synthetic rubber including, for example, butadiene-styrene copolymer rubber presently referred to in the art as SBR rubber, Buna-N rubber (NBR) produced from butadiene and acrylonitrile, butyl rubber produced from butadiene and isobutylene, neoprene, etc. The natural rubbers include Hevea rubber, caoutchouc, balata, guttapercha, etc. It is understood that the term rubber as used in the present specifications and claims is intended to include both synthetic rubber and natural rubber which undergo cracking due to ozone.

The following examples are introduced to illustrate further the novelty and utility of the present invention but not with the intention of unduly limiting the same.

EXAMPLE I Table I Ingredient: Parts by wt. SBR-1502 100 Furnace black 40 Zinc oxide 3 Stearic acid 2 Sulfur 2 Accelerator 1 l 1 N-cyclohexyl-2henzothiazole-sulfeneamide. A sample of the rubber of the above recipe was used as the blank or control sample. Different additives were incorporated in other samples of the rubber during milling as will be specifically set forth below. All of the samples were formed into strips 6 inches long, 0.75 inch wide and 0.08 inch thick and cured individually at 284 vF. The samples then were preaged at 194 F. for 0.1 and 2 days, after which different samples were elongated 10% or and evaluated in an ozone cabinet at 100 F. in an atmosphere containing 50 parts of ozone per 100 million parts of air. The samples were examined periodically and the time to first visible cracks was determined and is reported below.

All control samples underwent visible cracks within 2 hours of exposure in the ozone cabinet.

Samples of the rubber containing 2% by weight of a phenylenediamine antiozonant (N,N-di-2-octyl-pphenylenediamine) and elongated 10% did not undergo cracking for more than 168 hours in the ozone cabinet for the sample preaged for 1 day. However, the sample elongated 10% and preaged for 2 days underwent cracking within 24 hours. The samples elongated 20% and preaged for 1 or 2 days underwent cracking within 8 hours. The phenylenediamine antiozonant is very effective when used in this rubber formulation at concentrations of 4% or more by weight. For example, samples of the rubber containing 4% by weight of the N,N-di-2-octyl-p-phenylenediamine, elongated 10% and preaged for 0, 1 or 2 days did not undergo cracking for greater than 168 hours of exposure in the ozone cabinet and this is also true for the samples elongated 20% and preaged for 0 or 1 day. However, the sample elongated 20% and preaged for 2 days underwent cracking within 4 hours of exposure in the ozone cabinet.

EXAMPLE II When used in the base rubber described in Example I, the N-substituted p-aminophenol and N-substituted-palkoxyaniline possessed substantially no antiozonant potency. This is illustrated in the present and following examples in which different samples of the base rubber described in Example I were prepared to contain 2% by weight each of the following compounds described by the formula hereinbefore set forth. The different samples of the rubber were preaged, elongated 10% or 20% and evaluated in the same manner as described in the preceeding example.

The compound used in this preparation was N-secbutyl-p anisidine. When incorporated in a concentration of 2% by weight in another sample of the rubber and exposed in the ozone cabinet, all samples, whether elongated 10% and 20%, and preaged for 0 or 1 day. It is of exposure in the ozone cabinet. This demonstrates that this compound by itself possesses no antiozonant potency in the base rubber used in this example.

However, another sample of the same rubber containing 2% by weight of N-sec-butyl-p-anisidine and 2% by weight of N,N-di-2-octyl-p-phenylenediamine did not undergo cracking for more than 168 hours for the samples elongated 10% and 20% and preaged for 0 or 1 day. It is surprising that this mixture produced improved results over the use of 2% by weight of the phenylenediamine antiozonant above.

EXAMPLE III The compound of this example is N-sec-octyl-p-anisidine, prepared by the reductive alkylation of p-anisidine with ethyl amyl ketone. When samples of the base rubber described in Example I were prepared to contain 2% by weight of N-sec-octyl-p-anisidine, elongated 10% or 20%, preaged for 0, 1 or 2 days and evaluated in the ozone cabinet, all samples underwent cracking within 2 hours of exposure in the ozone cabinet.

This again demonstrates that this compound possessed no antiozonant properties in this particular base rubber.

Samples of the base rubber were prepared to contain 2% by weight each of N,N'-di-2-octyl-p-phenylenediamine and N-sec-octyl-p-anisidine and were evaluated in the same manner as described above. All of the samples elongated 10% and preaged at 0, 1 or 2 days did not undergo cracking for more than 168 hours of exposure in the ozone cabinet. The sample elongated 20% and preaged for 1 day also did not undergo cracking for more than 168 hours of exposure in the ozone cabinet. Here again, it is surprising that this mixture produced a synergistic effect.

EXAMPLE IV The compound of this example is N-Z-ethylhexyl-p- 'aminophenol. When 2% by weight of this compound was incorporated in another sample of the rubber described hereinbefore, elongated and evaluated in the same manner, all of the samples preaged for one or 2 days underwent cracking within 4 hours. On the other hand, other samples of the base rubber containing 2% by weight each of N,N'- di-2-octyl-p-phenylenediamine and N 2 ethylhexyl-paminophenol, did not undergo cracking for all of the samples elongated 10% and preaged 0, 1 or 2 days and the samples elongated 20% and preaged for 0 and 1 day for more than 168 hours of exposure in the ozone cabinet. Here again a synergistic eflect is observed.

EXAMPLE V The compound of this example is N-methyl-N'-n-butylp-aminophenol. When 2% by weight of this compound was incorporated in other samples of the base rubber described previously, the samples preaged for one and 2 days and elongated either 10% or 20% underwent cracking within 6 hours of exposure in the ozone cabinet. In contrast, other samples of the rubber containing both 2% by weight of N,N'-di-2-octyl-p-phenylenediamine and 2% by weight of N-methyl-N-n-butyl-p-aminophenol did not undergo cracking for more than 168 hours of exposure in the ozone cabinet for the samples elongated 10% and preaged 0 or one day and for the sample elongated 20% and preaged 0 day. Here again, the synergistic effect is demonstrated.

EXAMPLE VI The synergistic mixture of this example comprises 70% by weight of N,N'-dicyclohexyl-p-phenylenediamine and 35% by weight of N-methyl-N-sec-butyl-p-phenetidine. The synergistic mixture is incorporated in a concentration of 4% by weight during milling of the rubber and serves to improve the stability of the rubber against cracking due to ozone.

EXAMPLE VII The synergistic mixture of this example comprises 65% by weight of N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine antiozonant and 35% by weight of N-sechexyl-p-anisidine. The synergistic mixture is incorporated in a concentration of 4% by weight in natural rubber and serves to retard cracking of the ruber due to ozone.

EXAMPLE VIII The synergistic mixture of this example comprises 60% by weight of N-phenyl-N'-isopropyl-p-phenylenediamine where R and R are hydrogen or alkyl containing from one to about 20 carbon atoms, R" is hydrogen, alkyl containing from one to about 20 carbon atoms or cycloalkyl containing from three to about 12 carbon atoms and R is alkyl containing from one to about 20 carbon atoms or cycloalkyl containing from three to about 20 carbon atoms, said mixture comprising from about 50 percent to about 90 percent by weight of the phenylenediamine antiozonant derivatives and from about 50 percent to about percent by weight of the compound defined by the formula.

2. The mixture of claim 1 wherein said phenylenediamine antiozonant is N,N'-di-sec-octyl-p-phenylenediamine.

3. The mixture of claim 1 wherein said phenylenediamine antiozonant is N-phenyl-N-sec-hexyl-p-phenylenediamine.

4. The mixture of claim 1 wherein said compound defined by the formula is an N-alkyl-p-aminophenol.

5.The mixture of claim 1 wherein said compound defined by the formula is N,N-dialkyl-p-aminophenol.

6. The mixture of claim 1 wherein said compound defined by the formula is N-alkyl-p-alkoxyaniline.

7. The mixture of claim 1 wherein said compound defined by the formula is N,N-dialkyl-p-alkoxyaniline.

8. The mixture of claim 1 used as an antiozonant in rubber.

References Cited UNITED STATES PATENTS 2,865,723 12/1958 Lappin et al 252403 X 3,209,030 9/1965 Bicek 252403 X 3,288,749 11/1966 Cox 26045.9 3,304,284 2/1967 Cox 26045.9 3,304,285 2/1967 Cox 26045.9

MAYER WEINBLATI, Primary Examiner I. GLUCK, Assistant Examiner US. Cl. X.R. 

